Warm northern tropical Indian Ocean strengthened the ocean circulation prior to the last glacial termination

Abstract

Modern observations and model simulations suggest a strong influence of tropical processes on high-latitudinal climate. The evidence of similar tropics-high latitude climate link during glacial termination is, however, elusive. Here we show a strong influence of tropical processes in terminating the last glacial period based on multi-decadal seawater temperature, upwelling intensity and runoff records from the tropical Indian Ocean. We report a well-defined warming (1.4 °C) starting at ~20 kyr BP, coeval with abrupt increase in upwelling intensity and local CO2 outgassing, long before the beginning of increase in global atmospheric CO2 at 18.2 kyr BP. We suggest that the tropical Indian Ocean warming prior to the increase in global atmospheric CO2 was modulated by intense regional hydrographic changes caused by local summer insolation. The warming prior to Termination I (~18-11 kyr BP), at our site was synchronous with a small but evident strengthening of the Atlantic Meridional Overturning Circulation (AMOC). We conclude that the early warming in the tropical northern Indian Ocean led to stronger AMOC and the subsequent melting of the northern high latitude sea ice, which ultimately triggered the Heinrich Stadial during the last glacial termination